Fuel oil with improved flow properties

ABSTRACT

The response of a middle distillate petroleum fuel oil to the addition of a flow improver, such as a copolymer of ethylene, whereby flow and pumpability at low temperatures are improved, is increased by incorporating said fuel oil a small proportion of a paraffinic wax in sufficient quantity to furnish from about 0.03 to about 2 weight percent of normal paraffin hydrocarbons whose average molecular weight is within the range of from 300 to 650. The paraffinic wax that is added has a molar heat of fusion that is greater than the molar heat of fusion of the first wax that separates from the fuel upon cooling to or below its cloud point. Preferably, the added wax contains normal paraffin hydrocarbons ranging from n-C24 to at least n-C28 inclusive.

United States Patent [72] Inventors William C. Hollyday, Jr

Watchung; Nicholas Feldman, Woodbrldge, both of NJ. [21] App]. No. 760,346 [22] Filed Sept. 17, 1968 [45] Patented Nov. 16, 1971 [73] Assignee Esso Research and Engineering Company [54] FUEL 01L WITH IMPROVED FLOW PROPERTIES 7 Claims, No Drawings [52] 0.8. CI 44/62, 44/70, 44/80 [51] Int. CL. C101 l/16, C101 1/18 [50] Field of Search 44/62, 70, 80; 252/56, 59; 208/15, 17, 28, 33

[56] References Cited UNITED STATES PATENTS 2,177,732 10/1939 Maclaren 44/80 X 2,379,728 7/1945 Lieber et a1. 44/62 X 2,917,375 12/1959 Hudson 44/62 3,093,623 6/1963 11nyckyj.. 44/62 X 3,236,612 2/ 1966 llnyckyj 44/62 Primary Lxaminer-Daniel E. Wyman Assistant Examiner-W. J. Shine Attorneys- Pearlman & Stahl and Byron O. Dimmick ABSTRACT: The response of a middle distillate petroleum fuel oil to the addition of a flow improver, such as a copolymer of ethylene, whereby flow and pumpability at low temperatures are improved, is increased by incorporating said fuel oil a small proportion of a paraffinic wax in sufficient quantity to furnish from about 0.03 to about 2 weight percent of normal paraffin hydrocarbons whose average molecular weight is within the range of from 300 to 650. The paraffinic wax that is added has a molar heat of fusion that is greater than the molar heat of fusion of the first wax that separates from the fuel upon cooling to or below its cloud point. Preferably, the added wax contains normal paraffin hydrocarbons ranging from n-C to at least n-C inclusive FUEL OIL WITH IMPROVED FLOW PROPERTIES FIELD OF THE INVENTION This invention concerns an improvement in the low-temperature flowability of a middle distillate petroleum fuel through flow lines and filters wherein there is utilized a copolymer pour point depressant or flow improver of the type comprising a copolymer of ethylene with another ethylenically unsaturated monomer, such as an unsaturated ester or another olefin, wherein the ethylene fonns a backbone along which there are randomly distributed side chains consisting of hydrocarbon groups or of oxy-substituted hydrocarbon groups of up to 16 carbon atoms. It has been found in accordance with this invention that the response of a middle distillate fuel oil to the addition of a flow improver of the types'mentioned will be greatly improved if there is added to the fuel oil a small proportion of a paraffin wax having a molar heat of fusion which is greater than the molar heat of fusion of the first wax which separates from the untreated fuel when the fuel has been cooled to or below its cloud point.

DESCRIPTION OF THE PRIOR ART The use of copolymers of ethylene and other polar monomers such as vinyl esters, acrylate esters or methacrylate esters,-and the like to lower the pour point and improve'the fiowability of middle distillate fuels at low temperatures is well known in the art. See for example U.S. Pat. Nos. 3,037,850, 3,048,079, 3,069,245, 3,093,623 and 3,236,612.

DESCRIPTION OF THE INVENTION Heating oils and other middle distillate petroleum fuels, e.g. diesel fuels, contain small amounts of hydrocarbon waxes whichtend to precipitate in large interlocking crystals at low temperatures. These hydrocarbon waxes are largely normal paraffins. This interlocking of the crystals sets up a gel structure which causes the fuel to lose its fluidity. The lowest temperature at which the oil will still flow is generally known as the pour point. When the fuel temperature goes below the pour point and the fuel is no longer freely flowable, difficulty arises in transporting the fuel through flow lines and pumps, as for example when attempting to transfer the fuel from one storage vessel to another by gravity or under pump pressure or when attempting to feed thefuel into a burner. Additionally, the wax crystals that have come out of solution tend to plug fuel lines, screens, and filters. This problem has been'well recognized in the past and various additives have been suggested for depressing the pour point of the fuel oil. Onefunction of such pour point depressants has been to change the nature'of the crystals that precipitate from the fuel oil, thereby reducing the tendency of the wax crystals to interlock and set into a gel. It is believed that the pour point depressant additive functions not only by arresting wax crystal growth but also by destroying cohesive forces between the crystals. Even though a pour point depressant may function to lower the temperature at which the oil will no longer flow, waxcrystallization still occurs at a point above the pour point, i.e. at the cloud point, which is the point at which the oil becomes cloudy because of wax crystallization. Usually, the cloud point is not affected by the flow improver. Small-size crystals are desirable so that the precipitated wax will not clog the fine-mesh screens that are provided in fuel transportation, storage, and dispensing equipment. Pour point depressants that function by changing the wax crystals-to a more advantageous-size and shape can thus also be referredto as flow improvers. It is desirable to obtain not only fuel oils with low pour points but also fuel oils that will form small wax crystals so that the clogging of filters will not impair the flow of the fuel-at low operating temperatures.

In accordance with the present invention it is found that the response of a middle distillate petroleum fuel oil blend to a flow improver, particularly of the type comprising a copolymer of ethylene and another unsaturated monomer, is greatly improved by incorporating into the fuel oil a minor amount of a parafiin wax sufficient to impart to the fuel oil from 0.03 to 2 weight percent, and preferably from 0.1 to 2 weight percent, of normal paraffin hydrocarbons whose average molecular weight is within the range of from 300 to 650. The wax that is added is further characterized by having a heat of fusion that is greater than the heat of fusion of the first wax that separates from the untreated fuel when it is cooled to or below its cloud point. The heat of fusion of the wax will be in the range of about 15,000 to 42,000 calories per ,mole. Preferablythe heat of fusion of the wax will be'from 3,000 to 1 1,000 calories per mole greater than the heat of fusion of the first wax to'precipitate on cooling from the fuel before the fuel has been treated.

The paraflin wax that is used for modifying a middle distillate fuel oil in accordance with theinvention can consist of normal paraffins ranging from as low as C l-I up to an average of about C li with individual n-paraffins in the mixture ranging as high as 50 to 60 carbon atoms. Preferably the number averagemolecular weight'of the wax should be in the range of about 350 to 450. While it is possible to use individual parafi'in hydrocarbons in practicing the invention,

- better results are usually obtained with a wax comprising a mixture of hydrocarbons. Furthermore, it is ordinarily not economic to employ individual normal paraffin hydrocarbons in the wax range.

Particularly effective wax mixtures for distillate fuel oils having final boiling points in the range of 620 to 670 F are those that have normal paraffin hydrocarbons in the range of C to C inclusive. The waxes that are added include both well defined waxes and crude waxes, such as slack wax and slop wax, as well as any of the various refinery streams wherein wax is a-predominant constituent. The waxes that are used have a heat of fusion of from 40 to 55 calories per gram, and are thus distinguished from petroleum resins, asphaltenes,

petrolatums, and microcrystalline waxes, all of which have tially. Thus a typical-heating oil having an atmospheric distillation final boiling point of 640 F. will contain n-paraffins from about C to about C with very little C and higher n-paraffins. The wax which separates from this fuel oil when it is cooled to and below its cloud point will contain this spread of normal parafifins. To improve the low-temperature response of this fuel oil to allow improver, a parafiin wax can be added that contains C and higher'n-parafiingwith the average in the range of C to C While it would be possible for the refiner to introduce higher normal parafiins into the fuel oil simply by increasing the final boiling point of some of the fuel oil components, this would have the disadvantage of making the fuel oil color-unsuch a procedure would have a further disadvantage in that there would be no control over the amount of higher molecular weight waxesthat would be introduced and the desired improvement in low-temperature response would not be obtained.

Ideally, the paraffin wax that is used in the practice of this invention is selected on the basis of the thermodynamic properties of the -wax which separates from the fuel to be treated. The choice depends upon'a relation between the enthalphy and entropy of fusion of the precipitating wax and the n-paraffinic wax or wax'mixture that is to be-used. It is possible to characterize the fuel by the following method.

Cloud points of the fuel and of a blend of the fuel diluted with a hydrocarbon solvent are observed and the heat of fusion of the first wax to precipitate is calculated by the formula:

Here

AH Heat (enthalpy) of fusion T= Original cloud point of fuel (A) T,, Cloud point of dilute blend (A) AT= Difference in cloud points 8 Dilution ratio as grams of solvent per gram of fuel M Molecular weight of fuel M, Molecular weight of solvent Suitable solvents include naphtha, or preferably iso-octane (2,2,4 trimethyl pentane) of 1 l4 molecular weight.

M, (the molecular weight of the fuel) can be measured by ebulirnetric, cryoscopic or osmometric methods. M can also be estimated from distillation data by the formula: Mq T+F 200) 4, where T is the distillation temperature at 10 percent over and F is the distillation temperature at 50 percent over in F. For practical purposes M may be assumed to be about 200 for No. 2 middle distillate fuels.

The following method can be used to characterize the added wax. Cloud points of two blends of the wax in a hydrocarbon solvent (such as iso-octane) are observed, and t the heat of fusion is calculated by the formula:

T Tg AT Where T, and T, are the observed cloud points in A and p and p, are the weight percent wax in each blend. The factor 1.03 corrects for the difference in molecular weights of the waxes of interest in this invention and suitable solvents such as naphtha or iso-octane.

Very crude waxes and waxy materials which contain appreciable amounts (even more than 50 percent) non-n-paraffins may also be characterized by this method.

As previously stated, the wax to be added is selected so that it will have a heat of fusion which is greater than that'of the first wax which separates from the fuel, with a value of 42,000 calories per mole as the upper limit. Preferably the wax has a heat of fusion which is 3,000 to 11,000 calories greater than that of the wax which precipitates from the fuel at the cloud point. In some instances optimum results can be obtained with a blend of two or more wax fractions.

The distillate fuel oils that can be improved by this invention include those that have boiling ranges at atmospheric pressure within the limits of about 250 to about 670 F. The distillate fuel oil can comprise straight run or virgin stocks, or thermally and/or catalytically cracked petroleum fractions or a blend in any proportion of straight run and cracked distillates.

The most common petroleum middle distillate fuels are kerosene, diesel fuels, jet fuels and heating oils. They are more fully described in such specifications as MlL-F-25558B (USAF) for turbo jet fuels, ASTM D-396-67 for fuel oils and ASTM D-97567 for diesel fuel oils. Since jet fuels are normally refined to very low pour points there will be generally no need to apply the present invention to such fuels. The lowtemperature flow problem is most usually encountered with diesel fuels and heating oil. The specifications for a representative No. 2 heating oil include a 10 percent ASTM distillation point no higher than about 440 F., and a 50 percent distillation point no higher than about 520 F., and a 10 percent boiltng point of at least 540' F. and no higher than about 640 to 650 F Heating oils are preferably made of a blend of virgin distillate, e.g. gas oil, naphtha, etc., and cracked distillates, e.g. catalytic cycle stock.

It is not intended that this invention be limited by any theory regarding its operation It may be that the addition of the normal paraflin waxes to the fuel oil serves to shift the distribution curve of the waxes in the fuel oil. in any event, the addition of the higher members of the n-paraffinic homologous series that are not originally present in the fuel oil unexpectedly hrtngs about the desired modification of the size and shape of the wax crystals as the fuel oil is cooled in the presence of the flow rmprover and thus accomplishes the desired result The pour point depressants or flow improvers that are employed in this invention are of the type comprising a copolymer of ethylene and at least one secondunsaturated monomer. The second unsaturated monomer can be another monoolefin, e.g. a C, to C alpha-monoolefin or it can be an unsaturated ester, as for example vinyl acetate, vinyl butyrate, vinyl propionate, lauryl methacrylate, ethyl acrylate or the like. (See Canadian Pat. Nos. 676,875 and 695,679). Other monomers include N-vinyl pyrrolidone (See Canadian Pat. No. 658,216). The second monomer can also be a mixture of an unsaturated mono or diester and a branched or straight chain alpha monoolefin. Mixtures of copolymers can also be used. as for example mixtures of a copolymer of ethylene and vinyl acetate with an alkylated polystyrene or with an acylated polystyrene (see US. Pat. Nos. 3,037,850 and 3,069,245). Stated more generally, a copolymer pour depressant useful in this invention will consist essentially of about 3 to 40, and preferably 3 to 20, molar proportions of ethylene per molar proportion of the ethylenically unsaturated monomer, which latter monomer can be a single monomer or a mixture of such monomers in any proportion, said polymer being oil soluble and having a number average molecular weight in the range of about 1,000 to 50,000, preferably about 15,000 to about 5,000 molecular weight. Molecular weights can be measured by cryoscopic methods or by vapor phase osmometry, for example by using a Mechrolab Vapor Phase Osmometer Model 310A.

The unsaturated monomers, copolymerizable with ethylene include unsaturated acids, acid anhydrides, and mono and diesters of the general formula:

R, I l;

wherein R, is hydrogen or methyl; R, is a-OOCR, or-CO0R, group wherein R is hydrogen or a C, to C preferably a C, to C, straight or branched chain alkyl group and R, is hydrogen OR-CO0R,. The monomer, when R, to R, are hydrogen and R, is-00C& includes vinyl alcohol esters of C, to C monocarboxylic acids. Examples of such esters include vinyl acetate, vinyl isobutyrate, vinyl laurate, vinyl myristate, vinyl palmitate, etc. When R, is-COOR, such esters include C, Oxo alcohol acrylate, methyl acrylate, methyl methacrylate, lauryl acrylate, isobutyl methacrylate, palmityl alcohol ester of alpha-methylacrylic acid, C Oxo alcohol esters of methacrylic acid, etc. Examples of monomers wherein R, is hydrogen and R, and R, are-00CR, groups, include mono C 0x0 alcohol fumarate, di-C, Oxo alcohol fumarate, di-isopropyl maleate; di-lauryl fumarate; ethyl methyl fumarate, fumaric acid, maleic acid, etc.

Other unsaturated monomers copolymerizable with ethylene to prepare pour point depressants or flow improvers useful in this invention include C, to C, branched chain or straight-chain alpha monoolef'tns, as for example propylene, noctene-l Z-ethyl decene-l n-decenel etc.

Small proportions, e.g. about 0 to 20 mole percent, of a third monomer, or even of a fourth monomer, can also be included in the copolymers, as for example a C, to C, branched or straight chain alpha monoolefin, e.g. propylene, n-octenel, n-decene-l etc. Thus, for example, a copolymer of 3m 40 moles of ethylene with one mole of a mixture of 30 to 99 mole percent of unsaturated ester and 70 to 1 mole percent of olefin could be used.

The copolymers that are formed are random copolymers consisting primarily of an ethylene polymer backbone along which are distributed side chains of hydrocarbon or oxy-substituted hydrocarbon.

The Oxo alcohols used in preparing the esters mentioned above are isomeric mixtures of branched chain aliphatic primarv alcohols prepared from olefins, such as polymers and copolymers of C to C. monoolefins, reacted with carbon monoxide and hydrogen in the presence of a cobalt-containing catalyst such as cobalt carbonyl, at temperatures of about 300 to 400 F., under pressures of about 1,000 to 3,000 p.s.i., to form aldehydes. The resulting aldehyde product is then hydrogenated to form the x0 alcohol, the latter being recovered by distillation from the hydrogenated product.

Any of the known methods for polymer preparation can be used in preparing the copolymer flow improver or pour depressant, including the techniques taught for ethylene-vinyl ester polymerizations in U.S. Pat. Nos. 3,048,479, 3,131,168, 3,093,623 and 3,254,063. However, a particularly useful technique is as follows: Solvent and a portion (e.g. to 50 percent of the total amount to be reacted) of each of the unsaturated monomers, that is to be copolymerized with the ethylene are charged to a stainless steel pressure vessel which is equipped with a stirrer. The temperature of the pressure vessel is then brought to reaction temperature and pressured to the desired pressure with ethylene. Then a catalyst, which can be dissolved in a solvent to aid in handling, and additional amounts of the comonomer or comonomers are added to the vessel periodically or continuously during the reaction time. Also during this reaction time, as ethylene is consumed in the polymerization, additional ethylene is supplied through a pressure-controlling regulator so as to maintain the desired reaction pressure fairly constant at all times. Following the completion of the reaction, the liquid phase of the contents of the pressure vessel is distilled to remove the solvent and other volatile constituents of the reacted mixture, leaving the polymer as residue. in general, based upon 100 parts by weight of polymer to be produced, about 100 to 600 parts by weight of solvent, and about 1 to parts by weight of catalyst, will be used.

The catalyst, or promoter, will generally be of the free radical type, including organic peroxide types such as benzoyl peroxide, diacetyl peroxide, ditertiary butyl peroxide, dicumyl peroxide, tertiary butyl perbenzoate, di-lauroyl peroxide, tbutyl hydroperoxide, and also such non-peroxy compounds as azo-bis-isobutyronitrile, and the like.

The solvent can be any nonreactive organic solvent for furnishing a liquid phase reaction, preferably a hydrocarbon solvent such as benzene, hexane, or the like. The solvent should of course, be one that will not poison the catalyst or otherwise interfere with the reaction.

Temperatures and pressures employed may vary widely. For example, depending partly on the decomposition temperature of the catalyst, the temperature may range from 100 to 450 F., with pressures of 500 to 30,000 p.s.i.g. However, usually the temperature will range between about 160 and about 350 F. Relatively moderate pressures of 700 to about 3,000 p.s.i.g. will be used with vinyl esters such as vinyl acetate, whereas with esters that have a lower reactivity to ethylene, such as methyl methacrylate, somewhat higher pressures, e.g. 3,000 to 10,000 p.s.i.g. are more satisfactory. A superatmospheric pressure is employed which is at least sufi'lcient to maintain a liquid phase medium under the reaction conditions, and is sufficient to maintain the desired concentration of ethylene in solution in the solvent. In general, this pressure is attained by maintaining a continuous pressure on the reaction chamber through controlling the inlet feed of ethylene. The time of reaction will generally be within 1 to 10 hours, the reaction time being usually interrelated with the reaction temperature and pressure, and will also vary with the particular catalyst used.

The pour point depressant or flow improver is generally used in a concentration in the range of from about 0.001 to about 2 weight percent, preferably from about 0.005 to about 0.5 percent by weight, based on the weight of the fuel oil being treated.

The specific copolymer of ethylene and vinyl ester used in the working examples of the invention and referred to as flow improver A, consisted of about 65 weight percent of ethylene and about 35 weight percent of vinyl acetate, and the copolymer had a number average molecular weight of about 2,000 as measured by vapor phase osmometry. The copolymer was prepared by copolymerizing ethylene and vinyl acetate,

using di-tertiary-butyl peroxide catalyst etc. (See Belgium Pat. No. 673,566, and French Pat. No. 1,461,008).

A typical preparation of this copolymer is as follows:

A 3-liter stirred autoclave is charged with 1,150 ml. of benzene as solvent and 40 ml. of vinyl acetate. The vapor space of the autoclave is first purged with a stream of nitrogen, followed by a stream of ethylene. The autoclave is heated to about 300 F. while ethylene is pressured into the autoclave until a pressure of 950 p.s.i.g. is reached. Then, while maintaining a temperature of about 300 F. and 950 p.s.i.g. pressure, m1./hour of vinyl acetate and 30 m1./hour of a solution consisting of 23 weight percent t-butyl peroxide dissolved in 77 weight percent of benzene, are continuously pumped into the autoclave at an even rate. Vinyl acetate is injected over about minutes, while the peroxide solution is injected into the reactor over a period of about 150 minutes from the start of the injection. After the last of the peroxide solution is injected, the batch is maintained at 300 F. for an additional 15 minutes. Then, the temperature of the reactor contents is lowered to about R, the reactor is depressured, and the contents are discharged from the autoclave. The emptied reactor is rinsed with 1 liter of warm benzene (at about 120 F.) which is added to the product. The product mixture is then stripped of the solvent and unreacted monomers by blowing nitrogen through it while it is heated on a steam bath.

Flow improver B, referred to in the examples was prepared by the same general method as flow improver A, using ethylene, vinyl acetate, and a mixture of a-monoolefins having a range of 12 to 16 carbon atoms. The vinyl acetate and mixed olefins were fed into the reactor together during the course of the reaction. Specifically the initial charge to the reactor was 670 ml. of benzene and 32 ml. of vinyl acetate, the reaction pressure was 900 p.s.i.g., the reaction temperature was 220 F., the catalyst was lauryl peroxide, the mixture of 80 weight percent vinyl acetate and 20 weight percent mixed olefins was injected at the rate of 80 ml. per hour for minutes, and the total reaction time was minutes. The yield was 255 grams of copolymer. The copolymer in 47 weight percent solution in kerosene had a viscosity of 136 cs. at 100 F.

Flow improver C was a copolymer of 22 weight percent vinyl acetate, 8 weight percent of C Oxo alcohol diesters of fumaric acid, and 70 weight percent of ethylene, the copolymer having a number average molecular weight of 2,400 as measured by vapor phase osmometry.

Flow improver D referred to in the examples was a copolymer of ethylene and isobutyl acrylate of 2,400 number average molecular weight, the copolymer having about 7.2 ethylene units per mol of isobutyl methacrylate.

It will be understood that although the fuel oil blends tested in the following examples contained only pour depressant additives, other additives that are commonly used in distillate fuels can also be employed, including viscosity index improvers, rust inhibitors, antiemulsifying agents, antioxidants, sludge dispersants, dyes, dye stabilizers, haze inhibitors and so forth.

The invention will be further understood when reference is made to the following examples, which include preferred embodiments of the invention.

EXAMPLE 1 in this example, two paraffin wax cuts were employed, hereinafter referred to as wax l and wax ll. Wax l was obtained by dewaxing a light paraffinic distillate obtained from a San Joaquin waxy crude oil. Wax 11 was obtained by dewaxing the rafinate obtained from the phenol extraction of a neutral parafiinic distillate having a 100 F. viscosity of about 75 S.U.S.

The weight percent normal paraffin distribution in these two waxes was found by gas chromatographic analysis to be the following:

The oil is considered to have passed the test if more than 85 percent of the oil has gone through the screen at the end of 25 seconds. The results obtained when testing the various blends described are given in table I, which follows:

TABLE I Percent flow Percent used Improver Improver C D Carbon No. 16 17 18. 19' 20 21 22 23 24 25 26 27 28 29 30 31 32 Wait I 0.4 1.0 1.9 3.5 ,5.7 8.3 11.8 14.5 15.2 12.5 11.2 5.3 2.6 1.1 0.5 0.2 WaxII 0.7 1.2 1.8 2.8 4.3 6.8 9.5 11.0 13.0 12.2 7.7 .7 2.5 1.5 '0.8 0.5

Fuel oil blends were prepared by adding various weight perboiling point and 15 volume percent of heavy virgin naphtha centages of the flow improvers described above to either of boiling in the range of 290 and 430 F. is improved in lowtwo fuel oils, identified as fuel oils M and N, respectively. In 10 temperature flow properties by adding thereto 0.1l weight some cases either wax l or wax II was added to the fuel oil and percent of flow improver B, described above, together with in other cases no wax was added. 0.7 weight percent of a paraffin wax fraction having the fol- Fuel oil M was a blend of 80 volume percent catalytic cycle lowing percentages of C, and C normal paraffins: l2.5-C distillate and 20 volume percent naphtha, and had an ASTM I 5 l l.8-C, l0. l-C 6.7-C 3.4-C 20C 0.9-C,

D-86 boiling range of 368 to 654 F. and an ASTM cloud point of +1 5 F. EXAMPLE 3 5 12 g gg gf fizg f gfizi gz g t f A petroleum distillate fuel oil comprising a blend of straight h g g h d AS M run and cracked distillate stocks and having an initial boiling gigi g gzg F 26:2 g a g Dim 322? range of 20 point of 310 F. and a final boiling point of 665 F. is improved Each of the blends p p as described was sugjected to a in low temperature flowability by incorporating therein 0.14 fluidity test that has been found to give resultsin the laborato- Z: 2212;5 3:5525: fi ggggzzz Eggs? ais lzg fiz fg ii i f x i 21:32: g gg number average molecular weight of about 3,200 and having p P y p y 2 been prepared as described in British Pat. No. 993,744, and described, this test consists of allowing the test oil to flow by 0 8 Wei ht ercem ofwax described in exam 1 gravity through a standard sized opening for a set period of g p p time. Specifically this fluidity test was carried out in the fol- M E 4 (Part lowing manner: A ZOO-milliliter sample of the oil is cooled at a controlled rate of 4 F. per hour until an oil temperature of 0 w f j' P'evwuslyodescnbedt a 9' f R is reached, the latter being the temperature at which mg an inmal boilmg point of 36 4 F., a percen t distillation the test is run. The oil is then permitted to flow by gravity of 535 and a final boflmg pomtoof a clfmd through a 30-mesh screen of 9 millimeters diameter for 25 Pf of +24 and a Pomt f +20 charactenzed seconds. The volume percentage of oil that has flowed w1th {espect to the heat of fusion of the first wax to through the screen at the end of this time is then measured. 35 preclpltate asfouows:

Characterization of a Distillate Fuel 1. Number average molecular weight (Osometer): 21 l 2. Cloud point: +24.5 F. (269.03 A) Percent recovery in the test Fuel 011 N Nora-Percentages of additives are by weight; percent recovery is by volume.

The data in table I show that incorporation of a small quantity of either wax l or wax ll in either of the fuel oils was quite efiective in reducing significantly the amount of flow improver that was necessary in order to improve the low-temperature flowability of the fuel oils.

EXAMPLE 2 -A heating oil of 30.3 APl gravity and composed of 85 volume percent of catalytically cracked stocks of 660 F. final (Part B) Characterization of a Wax l Description of wax: 136 F. melting point 2. Cloud point of 4.602 weight percent wax in-iso-octane: 10

3. Cloud point 6r'0.9s2 weight percent wax in iso-octane: +44.0 F. (279.9 A)

4. Calculation:

279.9 292.1 1.03X4.602 X ("292.1 279.55 K982 AH=21,000 calories per mole EXAMPLE A middle distillate heating oil to which had been added 0.015 weight percent of a flow improver was subjected to a flow and plugging test. The flow improver was'of the same na- 25 of cracked stocks and had an initial boiling point of 340 F a 30 5 percent point of 424 F., a 50 percent point of 530 F a 95 measure of the efi'ective viscosity of the fuel, and thus an indication of its flow behavior. 3

The flow and plugging test was run as follows: The middle distillate fuel (about 3,500 ml.) contained in a l-gallon can is cooled to a test temperature below the cloud point over 5 to 8 hours and maintained at this temperature for to hours. The precooled test probe consisting of 150 cm. of 4.8 mm.

outside diameter (0.8 mm. wall) copper tubing fitted with an inlet machined from a l-inch brass cube is inserted into the fuel. The inlet is a right-angle cone, l-inch in diameter at the base, and at the top of the cone where it joins the upper tubing is an orifice one-sixteenth inch in diameter and one-sixteenth inch long. The fuel is drawn into and through the probe under 5 inches mercury vacuum, and its volume is measured in a suitable receiver.

A pass is 90 percent or more of the sample flowing with a drop in the vacuum at the end of the test (signifying no wax plug in the line). If a plug occurs at the inlet, it is released by increasing the vacuum momentarily or with a wire. A borderline result is at least 90 percent over with one wax plug at the end or during the test. A failure is less than 90 percent over, or two wax plugs.

With most fuel blends, the most severe test is that run just a few degrees below the cloud point. Thus for practical purposes, one test run at 2 to 5 F. below the cloud point will serve to differentiate good fuels which will perform well under winter conditions from bad fuels which will plug lines in cold weather.

The test results obtained in the present example are shown in table 11, which follows:

TABLE [I [Efiect or Added n-Paraflins in Flow and Plugging Test] Test Test, Percent Flow rate, Test Added n-parafiln N o. tomu, F. flowing niL/mln. rating 3 +11 1 (n no. 4 +10 2 (1) D0. 1 +15 3 (1) Do. 0.1% n-CuIlm 2 +14 93 (3) Borderline.

3 +11 J1 113 Pass. 1 :14 89 122 go. 2 13 7 103 n. 01% 3 +13 97 101 no. 4 +11 J8 97 D0. 1 +12 06 104 R0. 2 +11 115 103 0. 3 +11 97 103 no. I 4 +10 95 98 DO. 2 plugs. 1 plug.

percent point of 635 F. and a final boiling point of 654 F. The ASTM cloud point was +1 8 F. and the ASTM pour point was +10 F. Addition of the flow. improver lowered the pour point to 20 F.

Blends were prepared by adding to portions of the fuel oil, plus the 0.015 weight percent of flow improver, 0.1 weight percent of various purified waxes 24, 28 and 36 carbon atoms, respectively. The heats of fusion of the heating oil and of the individual waxes were as follows, in calories per mole.

Heating oil 14,350 n-C H 16,375 n 17.390 n-C H, 24,060

The flow and plugging test was developed to measure and predict the flow behavior of middle distillate fuels at low temperatures, and was based upon extensive winter field test data. Good correlation between this test and actual field test results has been found. In principle, a sample of the cold, waxy fuel is drawn under vacuum through a length of copper tubing with conical inlet. The conical inlet serves as a wax packing device which increases the severity of the test as far as plugging the line is concerned. The flow rate through the copper tubing is a As shown by-the data in table 11, a 24 carbon atom paraffin wax was just borderline in improving the response of the fuel oil to the flow improver, while the higher molecular weight waxes were quite effective in this respect.

EXAMPLE 6 A number of commercial parafiin waxes were evaluated for their efiect on improving the responsiveness of a middle distillate fuel oil to the addition of a flow improver. These waxes had the characteristics shownbelow in table 111.

are hown in Tables IV and V TABLE IV.n-PARAFF1N CONTENT OF WAXES {Weight Percent of Total n-Parafi'lns by Carbon Number] A B C Weight percent non n-paraffins.. 5. 9 7. 1 10. 5 3. 6 n-Parafiin carbon No.

TABLE V .n-PARAFFIN CONTENT OF WAX E IN TABLE III (Total Non n-Paratfins Approximately 50 Weight Percent) Weight Percent n-Parafllns by Carbon Number Various percentages of these waxes were added to samples of a middle distillate heating oil to which had been added various percentages of the flow improver described in Example 4. The heating oil was made up of 20 volume percent of straight run distillates and 80 volume percent of cracked distillates, and had an initial boiling point of 370 F., a 5 percent distillation point of 415 F., a 50 percent distillation point of 531 F., a 95 percent point of 632 F and a final boiling point of 644 F. The ASTM cloud point was +25 F. and the pour point was +20 F. The heat of fusion of the first wax to precipitate from the fuel was calculated as 13,400 calories per mole, using the method described above. Each of the blends, both with and without added wax, was subjected to a low-temperature fluidity test which was designed to measure the flow behavior of distillate fuels at temperatures below the cloud point. Briefly described, this test consists of allowing the test oil to flow by gravity through a standard-sized opening for a period of three minutes and then measuring the percent of the volume of oil which will flow through the opening during this period of time. The test apparatus is essentially an hourglass-shaped device having upper and lower chambers connected by a brass tube 2.25 mm. (0.10 inch) in diameter and 12.5 mm. long connecting the two chambers. A thin aluminum disc initially separates the chambers. The lower chamber of the test instrument is filled with ml. of the fuel to be tested. The fuel is cooled to a temperature below the predetermined cloud point of the fuel. Then a reading is taken of the volume of fuel in the test instrument and the sample container is inverted. After one minute of settling time, the disc is punctured so that oil is permitted to drain through the flow opening. The percentage of oil that drains through the opening in a period of 3 minutes is referred to as percent recovery. The test results are given in Table V] which follows.

TABLE Vl.-N-PARAFFIN WAXES AS (01.1) FLOW IMPROVERS Percent recovery (wt. per

The scope of this invention is defined by the appended claims. There is no intention to limit the invention to the specific examples. which have been presented by way of illustration.

What is claimed is:

l. A petroleum distillate fuel having a boiling range within the limits of about 250 and 670 F which has been improved with respect to its low temperature flow properties by adding thereto:

from about 0.001 to about 2 weight percent of an oil-soluble wax-modifying random copolymer of ethylene and at least one additional ethylenically unsaturated polymerizable monomer, said copolymer having an average molecular weight of from about 1,000 to 50,000 and comprising about 3 to 40 molar proportions of ethylene per molar proportion of other monomers, said copolymer consisting primarily of an ethylene polymer backbone along which are distributed side chains of hydrocarbon or oxy-substituted hydrocarbon, said other monomers being selected from the group consisting of an alpha monoolefm of three to 16 carbon atoms; N-vinyl pyrrolidone; and an unsaturated acid, unsaturated acid anhydride, unsaturated monoester, or unsaturated diester, of the general formula:

B1 II wherein R is hydrogen or methyl; R, is a -00CR, or-COOR, group wherein R is hydrogen or a C to C straight or branched chain alkyl group and R, is hydrogen or-COOR,,

and a parafiin wax in an amount sufficient to incorporate into the said fuel oil from about 0.03 to about 2 weight percent of normal paraffinic hydrocarbons of number average molecular weight in the range of about 300 to 650, the molar heat of fusion of said added wax being greater than the molar heat of fusion of the first wax to separate from the said fuel when cooled.

2. Improved petroleum distillate fuel as defined by claim 1 wherein said copolymer is a copolymer of ethylene and an unsaturated ester.

3. Improved petroleum distillate fuel as defined by claim I wherein said copolymer is a copolymer of ethylene and another olefin.

4. Improved petroleum distillate fuel as defined by claim 1 wherein said copolymer is a copolymer of ethylene and vinyl acetate.

5. Improved petroleum distillate fuel as defined by claim 1 wherein said copolymer is a terpolymer of ethylene, vinyl acetate, and aliphatic alcohol diester of fumaric acid.

6. Improved petroleum distillate fuel as defined by claim 1 wherein said added wax has a molar heat of fusion that is from wherein said added wax includes normal paraffin hydrocar- 3,000 to 11,000 calories per mole greater than the molar heat bons in the range of C to C inclusive. of fusion of said first wax that separates from said fuel.

7. improved petroleum distillate fuel as defined by claim 1 e 

2. Improved petroleum distillate fuel as defined by claim 1 wherein said copolymer is a copolymer of ethylene and an unsaturated ester.
 3. Improved petroleum distillate fuel as defined by claim 1 wherein said copolymer is a copolymer of ethylene and another olefin.
 4. Improved petroleum distillate fuel as defined by claim 1 wherein said copolymer is a copolymer of ethylene and vinyl acetate.
 5. Improved petroleum distillate fuel as defined by claim 1 wherein said copolymer is a terpolymer of ethylene, vinyl acetate, and aliphatic alcohol diester of fumaric acid.
 6. Improved petroleum distillate fuel as defined by claim 1 wherein said added wax includes normal paraffin hydrocarbons in the range of C24 to C28 inclusive.
 7. Improved petroleum distillate fuel as defined by claim 1 wherein said added wax has a molar heat of fusion that is from 3, 000 to 11,000 calories per mole greater than the molar heat of fusion of said first wax that separates from said fuel. 